The molecular basis of photoreceptor cell outer segment disk membrane function will be studied using physical optics techniques. Birefringence measurements provide in situ information about the crystalline nature of outer segment disk membrane structure and about how the membranes are organized. Dichroism measurements provide information about how visual pigment is organized in the outer segment membranes. Such optical techniques are time resolvable, making it possible to study light-induced structure changes in the visual pigment molecules and the outer segment membranes that are fast enough to be related to visual excitation. Specific objectives of the research are to quantitate how outer segment microstructure is reflected in observed birefringence, how light-induced birefringence changes are related to the physiological processes of the photoreceptor cell, and how measured dichroism is related to visual pigment orientation in the desk membranes.